Deletions of the short arm of human chromosome 9 (9p) are frequently associated with leukemia and certain solid tumors. Evidence from different sources indicate that a tumor suppressor (TS) gene is located on chromosome 9 at band 9p22, the shortest region of overlap (SRO) of the deletions. The SRO has been narrowed down by the applicants to a genomic region smaller than 1000 kb located between the interferon gene cluster and the methylthioadenosine phosphorylase gene. The interferon genes have been excluded as the relevant TS genes in these deletions. The general objective of this project is to clone and characterize this TS gene and to explore its role in leukemogenesis. The specific aims of the project are: 1) To further define the limits of the SRO of the deletions and to clone genomic DNA sequences from within the SRO, Genomic DNA sequences will be obtained by genomic walking with Yac clones, and by cloning DNA sequences, PCR-amplified from 9p22 microdissected material. These DNA sequences will be assigned to the SRO by deletion mapping, and will be linked on a long range physical map. 2) To identify transcription units in genomic sequences from within the SRO, by using the criteria of interspecies conservation of nucleotide sequence, proximity to CpG islands, and identification of transcripts on northern blots. To test for alterations in the expression of such transcripts in different neoplastic cell lines or primary cell samples with without identified deletions. The absence of, or abnormal expression of transcripts in neoplastic cells, will identify the putative TS genes. 3) To clone the transcription units from the SRO, by screening cDNA libraries with the genomic probes that identify the relevant transcripts. 4) To characterize these transcription units in terms of their TS activity when introduced into cells with deletions by transfection in expression vectors. 5) Once the TS gene is identified, to compare it to other genes, and to explore its possible functions, and its role in development, cell senescence, cell differentiation, cell proliferation, and leukemogenesis. 6) To explore the possible interactions of this TS gene with other oncogenes, and its specific contribution to the leukemogenic process. Since these deletions are very frequent in a large variety of neoplasia, the associated TS gene may be a central player in oncogenesis, as seems to be the case for the p53 gene, and its characterization will be important for our understanding of the oncogenic process.